Republican Rep. Richard Pombo of Tracy, once expected to cruise to re-election after easily subduing a primary challenge, now finds his House seat threatened by the Democratic wave that seems to be building across the country.

Analysts say the contest for Pombo's district, which includes much of San Joaquin County and parts of three Bay Area counties, has tightened and national Democrats announced Tuesday that they have purchased television time for their first ads opposing the seven-term Republican lawmaker, who is chairman of the House Resources Committee.

"It's become clear that this race is close (and) that it's about more than just the district. It has become nationalized," said Robert Benedetti, a political science professor at University of the Pacific in Stockton.

One of the best indicators of that, he said, is the money pouring into the contest.

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When the campaign ends, the race between Pombo and Democrat Jerry McNerney, 55, a Pleasanton wind energy consultant, is expected to have cost upwards of $10 million, making it one of the priciest congressional battles ever in California, say campaign strategists.

Pombo first won election in 1992 and breezed to victory six more times. But this race is proving much more difficult, with national groups targeting the incumbent and polls showing Democrats poised to win at least the 15 net seats they need to take the majority in the House.

Registered Republicans outnumber Democrats 46 percent to 39 percent in Pombo's district, made up of parts of San Joaquin, Alameda, Contra Costa and Santa Clara counties. George W. Bush won the district in 2000 and 2004, but newcomers have been moving in from the more liberal parts of the Bay Area, which analysts say could tilt the political balance.

The incumbent also is hurt by the electorate's souring view of the Iraq war and the scandal-rocked House under GOP leadership.

"There is clearly a wave building in favor of the Democrats, and if it continues over the next two weeks, Pombo could be swept up," predicted UCLA political scientist Barbara Sinclair, an expert on Congress.

Two years ago, Pombo beat McNerney 61 percent to 39 percent.

A poll released in late September by the Defenders of Wildlife Action Fund, an environmental group bent on defeating Pombo, showed McNerney leading Pombo 48 percent to 46 percent -- a statistical dead heat.

Pombo's camp has conducted polls but has not released the findings. Still, said campaign spokesman Brian Kennedy, Pombo "is up in every poll we've done."

The Republican National Congressional Committee also has polled, and poured more money into the race to attack McNerney shortly thereafter, federal campaign records show.

The candidates are locked in a battle over the voters not affiliated with either of the major parties, a sizable chunk at 15 percent of the district's electorate, and McNerney, hammering on the "it's-time-for-a-change" theme, hopes to win a portion of the 38 percent of Republicans who voted for Pombo's two rivals in the June primary.

Pombo, 45, has deep political roots and a well-known family involved in ranching and real estate in the district, the majority of which is located east of the Altamont Pass. He also will be aided by the Republican Party's successful get-out-the-vote apparatus and an edge in campaign cash heading into the final days.

Pombo paints McNerney as a tax-loving ultraliberal "who thinks the war on terror is a joke," according to one of the congressman's radio ads.

McNerney has cast Pombo as a "rubber stamp for the worst excesses of the Bush administration" who supports the war in Iraq without question and who wants to unravel federal environmental protections.

Federal campaign records show that as of Sept. 30, Pombo had more than $1.1 million in cash on hand compared with McNerney's $323,798.

The records also show that overall, Pombo had raised $3.4 million and McNerney had raised $1.2 million. But the candidates have been collecting even more campaign cash in the past three weeks, including the estimated $400,000 Pombo raised at an event in Stockton headlined by President Bush.

More money is being spent in the form of independent expenditures by special interest groups and the political parties.

Environmental groups, such as the Sierra Club, have spent nearly $1 million to unseat the incumbent, who from his powerful committee post has championed proposals to alter the Endangered Species Act, allow states to drill in offshore waters and increase logging on federal lands.